They'd better find a good pretext for having Ripley going off into space again after the events of Alien and especially Aliens--when she was promised she'd just be an advisor protected by a military escort--only to basically do the second movie over again and not be distrustful of anyone saying that they'd like to go check out the Alien homeworld.
Don't get me wrong, I'm fine with the idea of undoing Alien 3 and Resurrection as long as they keep the character of Ellen Ripley consistent. They just are going to have to come up with a reason for Ripley to go into space again considering that now that Weaver is a grandma means that Ripley would have to be out of cryosleep for about 30 years by the time of Alien 5 (or is it still considered 3 now? haha).
This implies that Ripley went on with her life after awakening from cryosleep and aged and if what I understand about going to the Alien homeworld is correct, would mean some corporate douche-hole (a la Carter Burke) would have to convince her yet again to go into space to deal with the aliens when Ripley clearly wanted nothing to do with them at the start of Aliens in the first place.
But none of it really matters; they want to make a movie with old actors and most people outside of the target demographic don't remember or care about the old movies anyway.